The present invention relates to a method and apparatus for the calibration of a balancing unit for the balancing of mounted vehicle wheels. Such apparatus includes a display unit for the magnitude and angular position of unbalance and circuitry for processing of unbalance vibrations picked up by transducers. Circuitry is also included for the processing of the angular position of the unbalance derived from the unbalance measuring unit. Unbalance compensation weights are used to compensate the unbalance on the vehicle wheel. Unbalance information displayed and stored during a measurement run is compensated by a correction weight of the indicated magnitude and indicated angular position. A check run is carried out, the results of which are stored and displayed, and the balancing procedure is discontinued when a tolerance limit is not exceeded.
Rotating machinery components in operation are subjected to wear because of dirt or abrasion and often show distortions as a result of false clamping. Such components are tested from time to time for smooth running within certain intervals by means of so-called trim balancing or field balancing. If possible, the dynamic balancing compensation obtained with stationary balancing machines should not be changed. Examples for such rotating components are universal joint driveshafts for large machinery, fans and blowers, turbines of stationary machines and automotive driveshafts, brake drums and wheels on vehicles as rotating components on moveable machinery.
Vehicle mounted wheels, if balanced on the vehicle, are often driven by means of a friction drive whereby the automobile is elevated on the axle to be investigated so that the wheel is free to rotate. Driving wheels of an automobile can also be driven, after being lifted, by means of the car's engine. No further preparation of the wheels with regard to balancing is done.
Balancing weights already in position remain on the wheel and additional balancing weights are positioned during the balancing of the vehicle mounted wheels. Removal of the originally positioned balancing weights is not done. Were these weights removed, the dynamic balance obtained on a stationary balancing machine would be affected.
In German Pat. No. DE-PS 30 17 240, a device is disclosed for the determination of the unbalance of mounted motor vehicle wheels in which a vibration transducer is provided for the measurement of the forces or vibrations caused by the unbalance of a vehicle wheel. The vehicle wheel is elevated and means is provided for rotating the elevated vehicle. A measuring device functions to determine the direction and magnitude of unbalance. The displayed value of unbalance is adjusted by means of two test runs, one run with and one run without a balancing weight of known magnitude. In order to accurately determine the unbalance of the vehicle mounted wheels, means are proposed through which directly, from the indicated magnitude of unbalance, the magnitude of the compensating weight to be installed can be determined. Also proposed is the provision of two parallel memories in which the values of unbalance are stored in both memories as to magnitude and direction during the first test run. A subsequent subtractor gives the difference between the values stored during the first measuring run and the measured values of the second measuring run. These differences are forwarded to an indicator. The measured and stored unbalance value is correctly shown on the display without an additional measuring run. By means of this device, the indication of the magnitude of unbalance is calibrated in measuring runs so that the unbalance compensation can be subsequently carried out on the vehicle mounted wheels.
Such a calibration of the balancing equipment is time consuming because of the absolute necessity of measurement and control runs. Furthermore, for such calibration the device of in DE-PS No. 30 17 240, two measurement runs are required, and this calibration is carried out only once per automobile. This necessarily leads to errors in compensation when, for instance, because of different wheel suspensions, different vibratory characteristics prevail for each wheel. To avoid this deficiency, each wheel would have to be measured by means of a measuring run and a control run and subsequently the unbalance measuring unit would have to be recalibrated. Furthermore, with this measuring unit, it is not possible to conclude as to the correct results based merely on the difference between the test and control run. The calibration run is mandatory.
U.S. Pat. No. 3,678,761 discloses method and means for the calibration of the unbalance measuring unit with respect to the vibratory characteristics of the automobile wheel to be investigated. For this a compensating weight is positioned on a known wheel location.
Based on the known weight and the already existing unbalance, the measured and displayed amount of unbalance and the angle of its position are adjusted by means of electrical adjustment controls until the display corresponds to the known magnitude.